<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        @keyframes myfirst {
            0% {
                transform: rotate(0deg);
            }


            100% {
                transform: rotate(360deg);
            }
        }

        .a {
            background-color: aqua;
            height: 200px;
            width: 200px;
            animation: myfirst 3s linear infinite;
        }
    </style>
</head>

<body>
    <div class="a">123</div>
</body>
<script>
</script>

</html>